If the hoisted state before and after the hoisting is divided into vertical (standing) and horizontal (horizontal or inclined) states, those whose state is changed before and after the lifting are required to be hoisted; the hoisting is also applicable to motionless single-crane lifting or oversized mass lifting, so both hoisting and single-crane lifting are the basic operations for mobile crane.
According to 9.1.4 in technical standards for construction of large equipment hoisting project, the crane hoisting technology should be in line with “lifting hook should be less than 3° during hoisting”; according to 12.2.13 in petrochemical engineering construction specification for lifting, “the bias angle of lifting hook should not exceed 3° when using a flow-type crane to hoist workpieces” (herein flow-type crane means the mobile crane).
The bias angle of lifting hook refers to the angle that pulley block lifting force line (namely, resultant force line, hereinafter inclusive) acted on the lifting hook deviates from the plumb line.
Mobile crane has a series of operating functions, such as hoisting, slewing, luffing and jib telescoping and walking according to the hoisting process; all operations should be conducted in a manner of vertical hoisting.
To date however, mobile crane lacks a function of vertical lifting display monitor, so crane drivers cannot determine whether the lifting pulley block is in a vertical state, which should be completed by the driver under the command of lifting commander according to hoisted object information from vertical lifting monitor, thus resulting in belated or inaccurate disadvantages, especially in dangerous lifting, and then it can be determined that the hoisting, especially the mobile crane with large-scale hoisting process apparatus is lacking of the vertical hoisting monitoring function, therefore, it is the first path for improving security operation of mobile crane to be equipped with the vertical hoisting monitoring function for the purpose of avoiding hoisting risks.
The verticality or bias angle of lifting hook is always detected from the detected tilt angle of the sling (steel wire rope of lifting hook, hereinafter inclusive) or detected vertical posture of lifting hook via machine vision technology; According to incomplete retrieval, in the early 1980s, there was a program that lifting hook bias angle was detected from the sling, which was released on Sep. 15, 1986 by Russian SU1257050A1 patent document. As shown in Attached FIG. 1 in SU1257050A1, clamp the triangle frame 1 to sling 5 via bilateral roller 3, the triangular frame 1 could rotate around pulley shaft 4 when the sling swings; an angle measuring apparatus 2 is set on the platform of triangular frame to detect the tilt angle of sling 5.
Since 2012, the followings have appeared: 201110387199.4 crane hoisting verticality bias measuring display apparatus and hoisting method, and 201310153481.5 lifting hook bias angle detecting, monitoring apparatus and crane, disclose that the angle measuring apparatus is installed on the plane perpendicular to the lifting force line of the lifting pulley block moving pulley guard plate to detect the bias angle of the hook.